Abstracts

Rationale: Although ictal SPECT has shown the high sensitivity of seizure localization, some of ictal SPECTs may be non-lateralizing or non-localizing. To investigate the usefulness of repeated ictal SPECTs and to find factors related to localizing results of ictal SPECT, we repeated ictal SPECT in partial epilepsy patients whose the 1st ictal SPECT was not localized. The subtracted ictal SPECT co-registered to MRI (SISCOM) was performed to measure the localizability of each ictal SPECT. Methods: We included 69 patients (33 males and 36 females, mean age 29.5±12.2 years) with partial epilepsy, who had repeated ictal SPECTs. SISCOM was performed using Analyze software. SISCOM results were considered as localizing when SISCOM results were concordant to the final location of epileptic focus by the presurgical evaluation. We compared seizure duration, tracer injection times, interictal and ictal scalp EEG patterns, the presence of secondary generalization, and epilepsy classification between the localizing and non-localizing SISCOM groups. Results: The 2nd SISCOM results were localizing in 43 (62.3%) patients and still non-localizing in 26 patients (37.7%). Radiotracer injection time was significantly shorter in localizing group (25.1±8.9 seconds) than non-localizing group (49.2±55.8 seconds) in the 2nd ictal SPECT (p=0.008). Furthermore, radiotracer injection time of the 2nd ictal SPECT was significantly shorter than the 1st ictal SPECT only in localizing group (36.8±23.8 seconds at the 1st and 25.1±8.9 seconds at 2nd ictal SPECT in localizing group, p=0.004). The percentage time of injection ([tracer injection time/ total seizure duration]x100%) in 2nd ictal SPECT was also shorter in localizing group than in non-localizing group (37.9±23.0% in localizing group; 72.3±46.2% in non-localizing group, p<0.001). The ictal EEG patterns at the time of injection were more localized at the 2nd injection than the 1st injection only in localizing SISCOM group (localized 18.6%, lateralized 18.6%, contralateral 2.2%, bilateral 37.2%, generalized 23.3% at 1st injection vs localized 63.1%, lateralized 10.9%, bilateral 7.0%, generalized 14.0% at the 2nd injection in localizing group, p<0.05). Epilepsy syndrome, seizure type or seizure duration during ictal SPECT were not significantly different between localizing and non-localizing SISCOM groups. Conclusions: Repeated SISCOMs were helpful for localizing epileptic focus in partial epilepsy patients who showed non-localizing SISCOM at the 1st injection. The most important factors for increasing the sensitivity of SISCOM were early injection time and localizing ictal EEG pattern at the time of injection.